The continued development of sophisticated electronic devices for data processing and communications systems is placing rigorous demands on electrical connectors. Increasing integration of solid state devices, combined with the need to increase the speed of data processing and communication systems, requires that connectors have higher densities, higher pin counts, and better electrical performance than in the past.
Density and pin count are often viewed interchangeably, but there are important differences. Density refers to the number of contacts provided per unit length. In contrast, the number of contact elements that can reasonably withstand the mating and unmating forces is referred to as the pin count.
As more functions become integrated on semiconductor chips or on flexible circuit substrates and more chips are provided on printed circuit boards (PCBs), each PCB or flexible circuit must provide more inputs and outputs (I/Os). The demand for more I/Os directly translates to a demand for greater density. In addition, many system components are capable of operation at faster speeds than previously. Faster speed can result in the generation of potentially interfering signals, i.e., crosstalk and noise. The connectors used in such high-speed board-to-board, board-to-cable and cable-to-cable communications may be treated for design purposes like transmission lines in which crosstalk and noise become significant concerns. Indeed, the electrical performance of high-speed board-to-board, board-to-cable and cable-to-cable communications is dependent upon the amount of crosstalk and noise introduced at the connector interface. As density increases, the potential for crosstalk and noise at the connector interface also increases.
Density, contact element count, and electrical performance are related to one another. Design factors should be balanced to optimize the connector in terms of its density, contact element count and electrical performance. Density can be increased by decreasing the distance between contact elements and by increasing the number of rows in a connector. Increasing the density may also increase the contact element count because 1) more contact elements are available for mating and unmating, and 2) higher density reduces the linear tolerances per contact element as mating and unmating forces are averaged over more contact elements. An increase in contact element density may, however, adversely affect the electrical performance of the connector since crosstalk can increase by bringing the contact elements into closer proximity to one another. The contact element count is limited in part by the mechanical forces applied when the connector is mated and unmated.
As was recognized in U.S. Pat. No. 4,824,383--Lemke, incorporated herein by reference, an important connector design consideration is the provision of an electrical connection while avoiding degradation of component performance. Prior to this patent, connector designs had been proposed in which a ground plane and alternating ground contacts together with shielding extensions were introduced to minimize electrical discontinuities, i.e., crosstalk and noise. While performance was controlled in such prior devices, density was limited.
U.S. Pat. No. 4,824,383 proposed designs for plug and receptacle connectors for multiple conductor cables or multiple trace substrates. In such designs individual contact elements or groups of contact elements were electrically isolated to prevent or minimize crosstalk and signal degradation. In the individually isolated design, a conductive base plate was provided with a number of walls arranged in side-by-side relationship, thereby defining a number of channels. A contact support member formed from electrical insulating material was designed to have a number of fingers, wherein a finger was positioned within each channel. Each finger of the contact support member supported an individual contact element. In the group isolated design, the base plate and walls defined channels for isolating sets of contact elements. Each set was carried by an enlarged finger of the contact support member. In this embodiment the base plate and walls were said to provide a ground plane to each contact element group, resulting in impedance control and lowered cross-talk. Both the individually isolated design and the group isolated design included a cover or shell formed from a conductive material, thereby providing additional isolation.
Although, the connectors disclosed in U.S. Pat. No. 4,824,383 increased contact element density, industry driven density demands continued to grow. In relation to meeting such demands, it was believed advantageous to provide an interconnection between the ground structure of the plug and receptacle connectors, to provide a structure to the receptacle that eliminated loose fits between the receptacle and contact element carrier and to provide a plug and receptacle whose interengaged signal contacts were disposed more closely to electrical ground. U.S. Pat. Nos. 5,057,028--Lemke et al. and 5,169,324--Lemke et al. (now U.S. Pat. No. Re. 35.508), all incorporated herein by reference, proposed designs to meet those objectives. In those patents, two row plug and receptacle connectors are described for attachment to printed circuit boards (PCBs), so that when such connectors are mated the PCBs are electrically interconnected.
The plug is described as preferably including a die-cast, metallic frame member having upper and lower crossbars connected at opposite ends by uprights. A central plate extends between the uprights in a plane generally parallel to the crossbars. The frame thereby defines two channels, namely upper and lower channels. The upper and lower channels are each described as being further divided by a central wall. Contact elements are embedded in extended fingers of insulating material. The extended fingers are inserted into each channel against the central plate and oriented such that the planar portion of each contact element is exposed. The contact elements thereby form two rows facing away from the central plate towards the crossbars. Tail portions of the contact elements extend rearwardly through partitions formed of insulating material for attachment to a PCB.
The receptacle is described as including a die-cast, metallic frame having an open front and rear. The frame includes upper and lower crossbars which are interconnected at corresponding ends by uprights. A central plate extends across the frame between the uprights in a generally planar relationship to the crossbars. The frame thereby defines two channels, namely upper and lower channels. The upper and lower channels are in turn divided at the midpoint by a further upright, thereby defining four sub-channels. A pair of insulating nosepieces are mounted to the front of the frame. A contact block, formed from insulating material, is designed to fit within each subchannel. Curve shaped, electrical contact springs are imbedded into each contact block. The number and design of the contact springs corresponds to the number and design of the contact elements in the plug. When a contact block is fitted into the receptacle frame, the curved contact end of each contact spring is positioned within a window formed in the nosepiece. Each window is designed to receive and support the curved forward end of the contact spring. The contact springs thereby form two rows wherein the curved portion of each contact spring faces away from the crossbars towards the central plate. The tail portions of the contact springs extend rearwardly from the contact block for attachment to a PCB.
As the plug and receptacle components are brought together, they are guided into aligned engagement by cooperative interaction between tapered ends, the central wall and guide slots. Such interaction serves to accurately align the contact elements in the plug with the contact springs in the receptacle.
While the connectors described above serve to satisfy certain density needs in the industry, industry driven density demands still continue to grow. Therefore, there is still a need to provide higher density plugs and receptacles which are capable of transmitting high frequency signals without degradation.
In meeting this continuing need, the present invention not only includes a novel connector structure that provides for increased contact element density, but also, permits connectors of this type to interconnect two PCBs in generally the same plane. In achieving this latter feature, the plug and receptacle of the connector are designed for right angle mounting, i.e., the front of the plug or receptacle is oriented in a plane at substantially a right angle to the PCB on which the plug or receptacle is mounted. Examples of right angle connectors have been proposed in the past, for example the connectors disclosed in U.S. Pat. Nos. 5,399,105--Kaufman et al., 5,169,343--Andrews, and Re. 32,691--Dola et al. However, none of those connectors are designed for nor concerned with high density contact elements.